Lithium cell based on lithiated transition metal titanates

ABSTRACT

An electrochemical active material contains a lithiated zirconium, titanium, or mixed titanium/zirconium oxide. The oxide can be represented by the formula LiM′M″XO 4 , where M′ is a transition metal, M″ is an optional three valent non-transition metal, and X is zirconium, titanium, or a combination of the two. Preferably, M′ is nickel, cobalt, iron, manganese, vanadium, copper, chromium, molybdenum, niobium, or combinations thereof. The active material provides a useful composite electrode when combined with a polymeric binder and electrically conductive material. The active material can be made into a cathode for use in a secondary electrochemical cell. Rechargeable batteries may be made by connecting a number of such electrochemical cells.

FIELD OF THE INVENTION

The present invention relates to lithium cells based on lithiatedtransition metal titanates. More particularly, it provides activematerials useful as a cathode (positive electrode) active material andan anode (negative electrode) active material for use in secondaryelectrochemical cells.

BACKGROUND OF THE INVENTION

Lithium batteries are prepared from one or more electrochemical cells.Non-aqueous lithium electrochemical cells typically include a negativeelectrode, a lithium electrolyte prepared from a lithium salt dissolvedin one or more organic solvents, and a positive electrode of anelectrochemically active material, typically a chalcogenide of atransition metal. During discharge, lithium ions from the negativeelectrode pass through the liquid electrolyte to the electrochemicallyactive material of the positive electrode, where the ions are taken upwith the simultaneous release of electrical energy. Thus on discharge,the positive electrode functions as a cathode, and the negativeelectrode as an anode. To reflect this fact, the terms “positiveelectrode” and “cathode” will be used interchangeably in the descriptionand claims, as will the terms “negative electrode” and “anode”. Duringcharging, the flow of ions is reversed so that lithium ions pass fromthe positive electrode through the electrolyte and are plated back ontothe negative electrode.

Recently, the lithium metal anode has been replaced with a carbon anodesuch as coke or graphite in which lithium ions can be inserted to formLi_(x)C₆. In the operation of the cell, lithium passes from the carbonthrough the electrolyte to the cathode where it is taken up just as in acell with a metallic lithium anode. During recharge, the lithium istransferred back to the anode where it re-inserts into the carbon.Because no metallic lithium is present in the cell, melting of the anodedoes not occur even under abusive conditions. Also, because lithium isreincorporated into the anode by insertion or intercalation rather thanby plating, dendritic and spongy lithium growth does not occur.Non-aqueous lithium electrochemical cells are discussed, for example, inU.S. Pat. Nos. 4,472,487, 4,668,595, and 5,028,500. These cells areoften referred to as “rocking chair” batteries because lithium ions moveback and forth between the insertion or intercalation compounds duringcharge/discharge cycles.

Known positive electrode active materials include LiCoO₂, LiMn₂O₄, andLiNiO₂. The cobalt compounds are relatively expensive and the nickelcompounds are difficult to synthesize. A relatively economical positiveelectrode is LiMn₂O₄, for which methods of synthesis are known. Thelithium cobalt oxide, the lithium manganese oxide, and the lithiumnickel oxide have a common disadvantage in that the charge capacity of acell comprising such cathodes may suffer a significant loss in capacity.That is, the initial capacity available (amp hours/gram) from LiMn₂O₄,LiNiO₂, and LiCoO₂ is less than the theoretical capacity becausesignificantly less than 1 atomic unit of lithium engages in theelectrochemical reaction. Such an initial capacity value issignificantly diminished during the first cycle operation and suchcapacity further diminish in successive cycles of operation. For LiNiO₂and LiCoO₂ only about 0.5 atomic units of lithium is reversibly cycledduring cell operation. Many attempts have been made to reduce capacityfading, for example, as described in U.S. Pat. No. 4,828,834 by Nagauraet al. However, the presently known and commonly used, alkali transitionmetal oxide compounds suffer from relatively low capacity. Therefore,there remains the difficulty of obtaining a lithium-containing electrodematerial having acceptable capacity without disadvantage of significantcapacity loss when used in a cell.

Japanese Patent No. 08180875 to Aichi Seiko discloses a lithiumsecondary battery having a cathode made of an active material consistingof a lithium metal titanate of structure LiTiMO₄ wherein M is manganese,iron, chromium, nickel, cobalt, magnesium, and/or boron.

Lithium ion technology, and the associated lithium containing compoundsuseful as cathode active materials in such batteries, have given theindustry needed flexibility in designing electrochemical cells for awide variety of technological uses. However, the industry is constantlyseeking for new materials to provide even greater flexibility in designparameters, ease of construction, and increased energy density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an x-ray diffraction pattern of LiVTiO₄ made from lithiumcarbonate.

FIG. 2 is an x-ray diffraction pattern of LiVTiO₄ made from lithiumhydroxide.

FIG. 3 is an x-ray diffraction pattern of synthesized LiCrTiO₄.

FIG. 4 is an x-ray diffraction pattern of synthesized LiMnTiO₄.

FIG. 5 is an x-ray diffraction pattern of synthesized LiFeTiO₄.

FIG. 6 is an x-ray diffraction pattern of synthesized LiCoTiO₄.

FIG. 7 is a first cycle constant current data of LiVTiO₄ made fromlithium carbonate.

FIG. 8 shows electrode voltage data for LiVTiO₄ made from lithiumcarbonate.

FIG. 9 shows a differential capacity data for LiVTiO₄ made from lithiumcarbonate.

FIG. 10 shows a first cycle constant current data of LiVTiO₄ made fromlithium hydroxide.

FIG. 11 shows electrode voltage data for LiCrTiO₄ as cathode.

FIG. 12 shows differential capacity data for LiCrTiO₄ as cathode.

FIG. 13 shows electrode voltage data for LiCrTiO₄ as anode.

FIG. 14 shows differential capacity data for LiCrTiO₄ as anode.

SUMMARY OF THE INVENTION

The present invention provides an electrochemical active materialcontaining a lithiated zirconium, titanium, or mixed titanium/zirconiumoxide. The oxide can be represented by the formula LiM′_(a)M″_(1−a)XO₄,where M′ is a transition metal or combination of transition metals, M″is a non-transition metal, a is greater than zero and less than or equalto 1, and X is zirconium, titanium, or combinations thereof. Preferably,M′ is titanium, nickel, cobalt, iron, manganese, vanadium, copper,chromium, molybdenum, niobium, or combinations thereof. The activematerial provides a useful composite electrode when combined with apolymeric binder and electrically conductive material. The activematerial can be made into a cathode for use in a secondaryelectrochemical cell. Rechargeable batteries may be made by connecting anumber of such electrochemical cells.

In another embodiment, some of the materials may also be used as anodematerials.

DETAILED DESCRIPTION OF THE INVENTION

The active material of the present invention contains a lithiatedtitanium or zirconium oxide of general formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

wherein M′ represents a transition metal or a mixture of transitionmetals, M″ represents a non-transition metal or a mixture ofnon-transition metals, a and b are independently greater than or equalto 0 and less than or equal to 1, and n ranges from about 0.01 to 2.When n is less than 1.0, M′ and M″ must take on an average oxidationstate greater than +3. When n is greater than 1.0, then M′ and M″ musttake on an average oxidation state less than +3. Preferably, n is atleast 0.2, and more preferably at least 0.5. In a preferred embodiment,n is about 1.0. Preferred transition metals include titanium, vanadium,manganese, iron, chromium, nickel, cobalt, molybdenum, niobium, andcombinations thereof. When b is 1 (i.e., when the active materials aretitanates), M′ comprises at least vanadium. When b is equal to zero(i.e., when the active materials comprise zirconates), and M′ istitanium, an active material of the invention may be represented byLiTiZrO₄. Representative non-transition metals include aluminum, boron,indium, gallium, antimony, bismuth, thallium, and combinations thereof.

The active material can be mixed with a polymeric binder and anelectrically conductive material to form an electrode material. Theelectrode material can then be made into an electrode using conventionaltechniques. In a preferred embodiment, the active materials of theinvention serve as cathode (positive electrode) active materials. Thecathode active material of the invention may be mixed or diluted withanother cathode active material, electronically conducting material,solid electrolyte, or compatible inert material. A cathode is readilyfabricated from individual or mixed cathode active materials.

In one aspect, the active materials of the invention are lithiumvanadium titanates of general formula

Li_(n)VTiO₄

wherein n is from 0.01 to about 2. In one embodiment, the activematerials are the source of lithium in a lithium ion battery. In such anapplication, n is preferably at least 0.2, and more preferably at least0.5. In a preferred embodiment, n is 1.0.

In another aspect of the invention, the active materials containlithiated metal zirconates or mixed titanates and zirconates of generalformula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

wherein a is from 0 to 1, inclusive, and b is less than one and greaterthan or equal to zero, n is from 0.01 to 2, M′ represents a transitionmetal or mixture of transition metals, and M″ represents anon-transition metal or mixture of non-transition metals. Preferably, nis at least 0.2, and more preferably at least 0.5. In a preferredembodiment, n is about 1.0. The transition metal M′ is preferablyselected from the group consisting of titanium, vanadium, manganese,iron, chromium, nickel, cobalt, molybdenum, niobium, and combinationsthereof. In a preferred embodiment, M′ is at least vanadium.

In yet another aspect of the invention, there are provided anode ornegative electrode active materials which are lithiated metal titanatesand/or zirconates represented by the general formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄,

wherein n is from 0.01 to about 2, a is greater than zero and less thanor equal to one, b is greater than or equal to zero and less than orequal to one, M′ is a transition metal or mixture of transition metals,and M″ represents a +3 non-transition metal or mixture of non-transitionmetals. Preferably, M′ comprises one or more transition metals selectedfrom the group consisting of titanium, vanadium, manganese, iron,chromium, nickel, cobalt, molybdenum, and niobium. In a preferredembodiment, M′ is at least chromium. Preferably, n is at least 0.2, andmore preferably at least 0.5. In a preferred embodiment, n is about 1.0.

Active materials having the formulas noted above are convenientlysynthesized by carrying out solid state reaction of starting materialswhich provide the metal elements and lithium of the active materials.For example, titanium and zirconium are conveniently provided astitanium dioxide and zirconium dioxide starting materials respectively.When the metals M, M′, and/or M″ are provided as oxide startingmaterials, the starting materials can be represented by the formulasM₂O₃, MO₂, and M₂O₅ for metals in an oxidation state of +3, +4, and +5respectively. It is also possible to provide the metals as hydroxides ofgeneral formula M(OH)₃, M(OH)₄ and the like for metals of differentoxidation states. A wide variety of materials is suitable as startingmaterial sources of lithium. One preferred lithium starting material islithium carbonate.

The solid state synthesis may be carried out with or without reduction.When the active materials are to be synthesized without reduction, thestarting materials are simply combined in a stoichiometric ratio andheated together to form active materials of the desired stoichiometry.Active materials having a range of values n for the lithium subscriptcan be made by providing metals M or mixtures of metals M′ and M″ inaverage oxidation states ranging from +2 (in which case n will be 2.0for charge balance), to +3 (in which case n will be 1.0 for chargebalance) up to about 3.9 (in which case n will be 0.1) or even up to3.99 (for n=0.01). For example, the titanium or zirconium may beprovided in the +4 oxidation state, while the metals M and alternativelyM′ or M″ are provided in a +3 oxidation state, for example as oxides orhydroxides, to form active materials where n is 1.0. When the solidstate reaction is carried out in the presence of a reducing agent, it ispossible to use metals as starting materials having initially higheroxidation states, and it is possible to incorporate lithium atnon-integer levels between about 0.01 and 2 as before. During thereaction, the oxidation state of the starting material metal is reduced.Either the reducing agent or the lithium compound can serve as limitingreagent. However, when the reducing agent is limiting, the activematerial will contain unreacted lithium compound as an impurity. Whenthe lithium containing compound is limiting, the reducing agent willremain in excess after the reaction. Commonly used reducing agentsinclude elemental carbon and hydrogen gas as illustrated below in theExamples. In the case of carbon as a reducing agent, the remainingexcess carbon does not harm the active material because carbon is itselfpart of the electrodes made from such active materials. When thereducing agent is hydrogen gas, any excess reducing agent is notincorporated into the starting material because the hydrogen volatilizesand can be removed. For these reasons, it is preferred to carry outreductive solid state reactions where the lithium compound is limitingin a stoichiometric sense. By selecting the amount of lithium compoundas limiting reagent, it is possible to prepare lithiated titanium orzirconium oxides of general formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

where n ranges from about 0.01 up to about 2. Formally, thetitanium/zirconium element is in a +4 oxidation state, while theoxidation state of M′ and M″ will take on an average oxidation state of+(4−n) to provide charge balance in the formula.

A preferred method of synthesis is a carbothermal reduction where carbonis used as reducing agent as discussed above. The reducing carbon may beprovided as elemental carbon, such as in the form of graphite or carbonblack. Alternatively, the reducing carbon may be generated in situduring the reaction by providing the reducing carbon in the form of aprecursor that decomposes or carbonizes to produce carbon during thereaction. Such precursors include, without limitation, cokes, starch,mineral oils, and glycerol and other organic materials, as well asorganic polymers that can form carbon material in situ on heating. In apreferred embodiment, the source of reducing carbon undergoescarbonization or decomposition at a temperature below which the otherstarting materials react.

Thus, the lithiated mixed metal titanates/zirconates of the inventioncan be prepared with a carbothermal preparation method using as startingmaterials a lithium source, a titanium and/or zirconium compound orcompounds, and a metal source. Examples of lithium sources includewithout limitation lithium acetate, lithium hydroxide, lithium nitrate,lithium oxalate, lithium oxide, lithium phosphate, lithium dihydrogenphosphate and lithium carbonate, as well as hydrates of the above.Mixtures of the lithium sources can also be used. Examples of metalsources include, without limitation, carbonates, phosphates, sulfates,oxides, hydroxides, carboxylates, acetates, silicates, and othercompounds of transition metals and non-transition metals. Non-transitionmetals include boron, the lanthanide series metals, and the alkalineearth metals, as well as the elements Al, Ga, In, Tl, Ge, Sn, Pb, Sb,Bi, and Po. Mixtures of metal sources may be used. Preferred metalsources include the oxides, dioxides, trioxides and hydroxides discussedabove. In a preferred embodiment, the metal source is chosen from amongcompounds of metals M′ and M″ as defined in the formula above. Thetitanium and/or zirconium compounds can be selected from a wide range ofcompounds, including those described above for the metal source, as wellas titanates or zirconates such as lithium titanate and lithiumzirconate. Preferred zirconium and titanium compounds include titaniumdioxide, zirconium dioxide, and combinations thereof.

In the carbothermal reductive method, the starting materials are mixedtogether with reducing carbon, which is included in an amount sufficientto reduce a metal ion of one or more of the metal-containing startingmaterials. The carbothermal conditions are set such as to ensure themetal ion does not undergo full reduction to the elemental state. Excessquantities of one or more starting materials other than carbon may beused to enhance product quality. For example, a 5% to 10% excess may beused. The carbon starting material may also be used in excess. When thecarbon is used in stoichiometric excess over that required to react asreductant with the molybdenum source, an amount of carbon, remainingafter the reaction, functions as a conductive constituent in theultimate electrode formulation. This is considered advantageous for thefurther reason that such remaining carbon will in general be intimatelymixed with the product active material. Accordingly, excess carbon ispreferred for use in the process, and may be present in a stoichiometricexcess amount of 100% or greater. The carbon present during compoundformation is thought to be intimately dispersed throughout the precursorand product. This provides many advantages, including the enhancedconductivity of the product. The presence of carbon particles in thestarting materials is also thought to provide nucleation sites for theproduction of the product crystals.

The starting materials are intimately mixed and then reacted togetherwhere the reaction is initiated by heat and is preferably conducted in anon-oxidizing, inert atmosphere. Before reacting the compounds, theparticles are mixed or intermingled to form an essentially homogeneouspowder mixture of the precursors. In one aspect, the precursor powdersare dry-mixed using a ball mill and mixing media, such as zirconia. Thenthe mixed powders are pressed into pellets. In another aspect, theprecursor powders are mixed with a binder. The binder is selected so asto not inhibit reaction between particles of the powders. Therefore,preferred binders decompose or evaporate at a temperature less than thereaction temperature. Examples include, without limitation, mineraloils, glycerol, and polymers that decompose to form a carbon residuebefore the reaction starts. In still another aspect, intermingling canbe accomplished by forming a wet mixture using a volatile solvent andthen the intermingled particles are pressed together in pellet form toprovide good grain-to-grain contact.

Although it is desired that the precursor compounds be present in aproportion which provides the stated general formula of the product, thelithium compound may be present in an excess amount on the order of 5percent excess lithium compared to a stoichiometric mixture of theprecursors. As noted earlier, carbon may be present in stoichiometricexcess of 100% or greater. A number of lithium compounds are availableas precursors, such as lithium acetate (LiOCOCH₃), lithium hydroxide,lithium nitrate (LiNO₃), lithium oxalate (Li₂C₂O₄), lithium oxide(Li₂O), lithium phosphate (Li₃PO₄), lithium dihydrogen phosphate(LiH₂PO₄), and lithium carbonate (Li₂CO₃). Preferred lithium sourcesinclude those having a melting point higher than the temperature ofreaction. In such cases, the lithium source tends to decompose in thepresence of the other precursors and/or to effectively react with theother precursors before melting. For example, lithium carbonate has amelting point over 600° C. and commonly reacts with the other precursorsbefore melting.

The method of the invention is able to be conducted as an economicalcarbothermal-based process with a wide variety of precursors and over arelatively broad temperature range. The reaction temperature forreduction depends on the metal-oxide thermodynamics, for example, asdescribed in Ellingham diagrams showing the ΔG (Gibbs Free EnergyChange) versus T (temperature) relationship. As described earlier, it isdesirable to conduct the reaction at a temperature where the lithiumcompound reacts before melting. In general, the temperature shoulddesirably be about 400° C. or greater, preferably 450° C. or greater,and more preferably 500° C. or greater. Higher temperatures arepreferred because the reaction generally will normally proceed at afaster rate at higher temperatures. The various reactions involveproduction of CO or CO₂ as an effluent gas. The equilibrium at highertemperature favors CO formation.

Generally, higher temperature reactions produce CO effluent while lowertemperatures result in CO₂ formation from the starting material carbon.At higher temperatures where CO formation is preferred, thestoichiometry requires more carbon be used than the case where CO₂ isproduced. The C to CO₂ reaction involves an increase in carbon oxidationstate of +4 (from 0 to 4) and the C to CO reaction involves an increasein carbon oxidation state of +2 (from ground state zero to 2). Here,higher temperature generally refers to a range above about 650° C. Whilethere is not believed to be a theoretical upper limit, it is thoughtthat temperatures higher than 1200° C. are not needed. Also, for a givenreaction with a given amount of carbon reductant, the higher thetemperature the stronger the reducing conditions.

In one aspect, the method of the invention utilizes the reducingcapabilities of carbon in a controlled manner to produce desiredproducts having structure and lithium content suitable for electrodeactive materials. The method of the invention makes it possible toproduce products containing lithium, metal and oxygen in an economicaland convenient process. The ability to lithiate precursors, and changethe oxidation state of a metal without causing abstraction of oxygenfrom a precursor is advantageous. The advantages are at least in partachieved by the reductant, carbon, having an oxide whose free energy offormation becomes more negative as temperature increases. Such oxide ofcarbon is more stable at high temperature than at low temperature. Thisfeature is used to produce products having one or more metal ions in areduced oxidation state relative to the precursor metal ion oxidationstate. The method utilizes an effective combination of quantity ofcarbon, time and temperature to produce new products and to produceknown products in a new way.

Referring back to the discussion of temperature, at about 700° C. boththe carbon to carbon monoxide and the carbon to carbon dioxide reactionsare occurring. At closer to 600° C. the C to CO₂ reaction is thedominant reaction. At closer to 800° C. the C to CO reaction isdominant. Since the reducing effect of the C to CO₂ reaction is greater,the result is that less carbon is needed per atomic unit of metal to bereduced. In the case of carbon to carbon monoxide, each atomic unit ofcarbon is oxidized from ground state zero to plus 2. Thus, for eachatomic unit of metal ion (M) which is being reduced by one oxidationstate, one half atomic unit of carbon is required. In the case of thecarbon to carbon dioxide reaction, one quarter atomic unit of carbon isstoichiometrically required for each atomic unit of metal ion (M) whichis reduced by one oxidation state, because carbon goes from ground statezero to a plus 4 oxidation state. These same relationships apply foreach such metal ion being reduced and for each unit reduction inoxidation state desired.

It is preferred to heat the starting materials at a ramp rate of afraction of a degree to 10° C. per minute and preferably about 2° C. perminute. Once the desired reaction temperature is attained, the reactants(starting materials) may be held at the reaction temperature for severalhours. Although the reaction may be carried out in oxygen or air, theheating is preferably conducted under an essentially non-oxidizingatmosphere. The atmosphere is preferably essentially non-oxidizing so asnot to interfere with the reduction reactions taking place. Anessentially non-oxidizing atmosphere can be achieved, for example,through the use of vacuum or inert gases such as argon. Although someoxidizing gas (such as oxygen or air) may be present, it should not beat so great a concentration that it interferes with the carbothermalreduction or lowers the quality of the reaction product. It is believedthat any oxidizing gas present will tend to react with the carbon andlower the availability of the carbon for participation in the reaction.To a large extent, such a contingency can be anticipated andaccommodated by providing an appropriate excess of carbon as a startingmaterial. Nevertheless, it is generally preferred to carry out thecarbothermal reduction in an atmosphere containing as little oxidizinggas as practical.

Advantageously, a reducing atmosphere is not required, although it maybe used if desired. After reaction, the products are preferably cooledfrom the elevated temperature to ambient (room) temperature (i.e., 10°C. to 40° C.). Desirably, the cooling occurs at a rate similar to theearlier ramp rate, and preferably 2° C./minute cooling. Such coolingrate has been found to be adequate to achieve the desired structure ofthe final product. It is also possible to quench the products at acooling rate on the order of about 100° C./minute. In some instances,such rapid cooling (quench) may be preferred.

The invention also provides for electrochemical cells made fromelectrodes containing the active materials described above. Anelectrochemical cell contains an anode and a cathode. In one embodiment,the electrochemical cells include a cathode containing the activematerial of the present invention and an intercalation based anode, withboth anode and cathode capable of reversibly incorporating, byintercalation or other insertion process, an alkali metal ion. Theelectrochemical cells also contain an electrolyte composition which in apreferred embodiment contains a polymeric matrix and an electrolytesolution. The electrolyte solution is made up of an organic electrolytesolvent and a salt of an alkali metal. Each electrode preferably has acurrent collector.

Rechargeable batteries of the invention may be made by interconnectingtwo or more electrochemical cells of the invention in an appropriateseries/parallel arrangement to provide the required operating voltage incurrent levels.

Lithium ion batteries containing cathodes having active materials of theinvention are generally operated according to known principles. Anelectrochemical cell is first provided in a discharged state. In thedischarged state, the cathode or positive electrode contains an activematerial based on a compound of general structure

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

wherein n is from about 0.01 to 2, a is greater than zero and less thanor equal to 1, and b is from 0 to 1. M′ comprises one or transitionmetals, preferably selected from the group consisting of titainium,vanadium, manganese, iron, chromium, nickel, cobalt, molybdenum, andniobium, with the proviso that when b is 1, M′ comprises at leastvanadium. M″ is selected from the group consisting of aluminum, boron,indium, gallium, antimony, bismuth, thallium, and combinations thereof.

The subscript n gives the number of lithium ions in the active materialof the invention. It can range from fractional values that are quitelow, up to values greater than 1 and as high as two. It can take onvalues between the two extremes according to the desired properties,such as theoretical specific capacity of the active material or thedischarge capacity of the battery. It is preferably greater than about0.5 and will commonly be close to or equal to 1.0.

After the electrochemical cell is provided as above in the dischargedcondition, it is put through a charging step to produce a battery in acharged or partially charged condition. Charging is generallyaccomplished by applying an outside electromotive force to the cell soas to cause the migration of lithium ions from the cathode to the anode.The anode contains an insertion or intercalation material such ascarbon. Migration of lithium ions to the anode results in insertion oflithium into the lattice of the insertion material. At the same time,lithium is removed from the cathode, until an amount c is removed. Whencharged, the anode thus contains insertion material with insertedlithium atoms. For example, when the insertion material of the anode isgraphitic, the inserted lithium atoms form a composition that can berepresented by the formula Li_(m)C₆, where m represents the fractionalcontent of lithium in the carbon environment. Correspondingly, thecathode in the charged battery has a lowered lithium content. Thecathode material can be represented as

Li_(n−c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

where c represents an amount of lithium ions removed or removable fromthe cathode during the charging step. In this example, it can be seenthat the cathode material in the uncharged and charged conditions can berepresented by the last formula above. In the (first) unchargedcondition, c is equal to 0. In the (second) charged or partially chargedcondition, c is greater than 0. It will be appreciated that in theformula above, c reaches a maximum value characteristic of the materialat the point at which the cell is fully charged. At intermediate stagesof the charging process, c takes on a value greater that zero but lessthan its maximum.

After charging, the cell is put through a discharging process.Typically, a load is applied to a circuit containing the battery orcell, and current flow from the battery or cell is used to operate theload. During discharge, lithium ions migrate to the cathode, along withelectrons (via the external circuit) that cause the reduction of thecathode material. Lithium ions are re-inserted into the cathode.Generally, a first cycle charge inefficiency is observed due, it isbelieved, to creation of a passivation film on the anode. On subsequentcycles with high-quality electrode or cathode materials, the amount oflithium extracted on charging will be approximately the same as theamount of lithium re-inserted on discharging. Cells containing suchhigh-quality materials are generally preferred because theirreversibility leads to a longer cycle life, so that the battery can becharged and re-charged a number of times.

When the active material of the invention is used as an anode material,the operation of the battery is similar. As before, the battery is firstprepared in a discharged condition, with the anode containing activematerial of formula

Li_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

where n, a, b, M′, and M″ are as defined above. The active materialserves as a lithium insertion material analogously to the carbonaceousinsertion anode described above.

After construction, the battery is first put through a charging process.During charging, lithium ions from the cathode migrate to the anode,where they are inserted in the active anode material to form a materialthat can be represented by the formula

Li_(n+c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

where c represents the amount of lithium inserted into the anode activematerial during the charging step. It can be seen that the anodematerial in the uncharged and charged states can be represented by thelast formula above. In the first (uncharged) condition, c is equal to 0.In the (second) charged condition, c is greater than 0. As before, creaches a maximum characteristic of the material at the point at whichthe cell is fully charged. At intermediates stages of charging, c takeson a value greater than 0 but less than its maximum.

After charging, the cell is put through a discharging process, asbefore. During discharge, lithium ions are re-inserted into the cathodematerial. With high quality anode materials, the amount of lithiuminserted during the charging step and the amount of lithium extracted ondischarge will be approximately the same so that a highly reversiblecell is formed, leading to long cycle life and re-chargeability in abattery, as indicated above.

Reversibility of electrochemical cells made with active materials of theinvention can be explained on a chemical basis as shown above. That is,in reversible cells, theoretically the amount of lithium being shuttledbetween the anode and cathode on successive charge/discharge cyclesremains relatively constant. The extent of the change in the amount oflithium transferred between electrodes over time can be observed inmeasurements of capacity fade.

In preferred embodiments, both the anode and cathode include a currentcollector that comprises, for example, a foil, a screen, grid, expandedmetal, woven or non-woven fabric, or knitted wire formed from anelectron conductive material such as metals or alloys. Particularlypreferred current collectors comprise perforated metal foils or sheets.In order to minimize the weight of the electrochemical cell, thincurrent collectors are preferred. Each current collector is alsoconnected to a current collector tab which extends from the edge of thecurrent collector. The anode tabs can be welded together and connectedto a lead. The cathode tabs are similar welded and connected to a lead.External loads can be electrically connected to the leads. Currentcollectors and tabs are described in U.S. Pat. Nos. 4,925,752,5,011,501, and 5,326,653, which are incorporated herein by reference.

In addition to the anode and cathode, the cells and batteries of theinvention contain an electrolyte composition. The electrolytecomposition generally contains from about 5 to about 25% preferably fromabout 10 to about 20%, and more preferably from about 10-15% of aninorganic salt wherein the percentages are based on the total weight ofthe electrolyte composition. The percentage of salt depends on the typeof salt and electrolytic solvent employed.

The inorganic ion salt of the electrolyte composition refers to any saltsuitable in a non-aqueous electrolyte composition. Representativeexamples of suitable inorganic ion salts are metal salts of less mobileanions of weak bases having a large anionic radius. Examples of suchanions include without limitation, I⁻, Br⁻, SCN⁻, ClO₄ ⁻, BF₄ ⁻, PF₆ ⁻,AsF₆ ⁻, CF₃COO⁻, CF₃SO₃ ⁻, N(SO₂CF₃)₂ ⁻, and the like. Specific examplesof suitable inorganic ion salts include, without limitation, LiClO₄,LiSCN, LiBF₄, LiAsF₆, LiCF₃SO₃, LiPF₆, (CF₃SO₂)₂NLi, (CF₃SO₂)₃CLi,NaSCN, and the like. The inorganic ion salt preferably contains at leastone cation selected from the group consisting of Li, Na, Cs, Rb, Ag, Cu,Mg and K.

The electrolyte composition further contains up to about 95 weightpercent of a solvent based on the total weight of the electrolytecomposition. The solvent of the electrolyte composition is generally alow molecular weight organic solvent added to the electrolytecomposition which may also serve the purpose of solvating the inorganicion salt. The solvent can in general be any compatible, relativelynon-volatile, and relatively polar aprotic solvent. Preferably, thesolvents have boiling points greater than about 85° C. to simplifymanufacture and increase the life of the electrolyte and battery.Typical examples of suitable solvents include organic carbonates as wellas other solvents such as gamma-butyrolactone, triglyme, tetraglyme,dimethylsulfoxide, dioxolane, sulfolane, and mixtures thereof. Whenusing propylene carbonate based electrolytes in an electrolytic cellwith graphite anodes, a sequestering agent, such as a crown ether, canbe added in the electrolyte.

Suitable organic carbonates are in general those with no more than abouttwelve carbon atoms, and which do not contain any hydroxyl groups.Preferably, the organic carbonate is an aliphatic carbonate and morepreferably a cyclic aliphatic carbonate.

Suitable cyclic aliphatic carbonates for use in this invention include1,3-dioxolan-2-one (ethylene carbonate); 4-methyl-1,3-dioxolan-2-one(propylene carbonate); 4,5-dimethyl-1,3-dioxolan-2-one;4-ethyl-1,3-dioxolan-2-one; 4,4-dimethyl-1,3-dioxolan-2-one;4-methyl-5-ethyl-1,3-dioxolan-2-one; 4,5-diethyl-1,3-dioxolan-2-one;4,4-diethyl-1,3-dioxolan-2-one; 4,4-dimethyl-1,3-dioxan-2-one;5,5-dimethy-1,3-dioxan-2-one; 5-methyl-1,3-dioxan-2-one;4-methyl-1,3-dioxan-2-one; 5,5-diethyl-1,3-dioxan-2-one;4,6-dimethyl-1,3-dioxan-2-one; and 4,4,6-trimethyl-1,3-dioxan-2-one.

Linear aliphatic carbonates are also suitable for use in the invention.Examples include, without limitation, dimethyl carbonate (DMC), dipropylcarbonate (DPC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC),and the like.

Several of these cyclic and linear aliphatic carbonates are commerciallyavailable such as propylene carbonate, ethylene carbonate, and dimethylcarbonate.

In one embodiment, the electrolyte composition also contains from about5 to about 30 weight percent, preferably from about 15 to about 25weight percent of a solid polymeric matrix based on the total weight ofthe electrolyte composition. In this embodiment, suitable solidpolymeric matrixes are well known in the art and include inorganicpolymers, organic polymers, or a mixture of organic polymers withinorganic non-polymeric materials. Suitable inorganic non-polymericmaterials include without limitation, β-alumina, silver oxide, lithiumiodide, and the like.

The anode of the electrochemical cells of the invention typicallycomprises a compatible anodic material which is any material whichfunctions as an anode in a solid electrolytic cell, such as, in certaincases, the anode negative active materials of the present invention.Other compatible anodic materials are well known in the art include,without limitation, lithium, lithium alloys, such as alloys of lithiumwith aluminum, mercury, manganese, iron, zinc, and insertion orintercalation based anodes such as those employing carbon, tungstenoxides, and the like. Preferred anodes include lithium insertion- orintercalation anodes employing carbon materials such as graphite, cokes,mesocarbons, and the like. Such carbon insertion-based anodes typicallyinclude a polymeric binder having a molecular weight of from about1,000-5,000,000, and optionally, an extractable plasticizer suitable forforming a bound porous composite. Examples of suitable polymeric bindersinclude, without limitation, EPDM (ethylene propylene diaminetermonomer), PVDF (polyvinylidene difluoride), EAA (ethylene acrylicacid copolymer), EVA (ethylene vinyl acetate copolymer), EAA/EVAcopolymers, vinylidene fluoride hexafluoropropylene copolymers, and thelike.

The cathode typically comprises a compatible cathodic material which isany material that functions as a positive pole in an electrolytic cell.The cathode of the present invention includes the lithiated transitionmetal zirconium or titanium oxides of the present invention, but mayalso include other cathodic materials. Such other cathodic materials mayinclude, by way of example, transition metal oxides, sulfides, andselenides, including lithiated compounds thereof. Representativematerials include cobalt oxides, manganese oxides, molybdenum oxides,vanadium oxides, sulfides of titanium, molybdenum and niobium, thevarious chromium oxides, copper oxides, lithiated cobalt oxides, e.g.,LiCoO₂ and LiCoVO₄, lithiated manganese oxides, e.g., LiMn₂O₄, lithiatednickel oxides, e.g., LiNiO₂ and LiNiVO₄, and mixtures thereof.Cathode-active material blends of Li_(x)Mn₂O₄ (spinel) is described inU.S. Pat. No. 5,429,890 which is incorporated herein. The blends caninclude Li_(x)Mn₂O₄ (spinel) and at least one lithiated metal oxideselected from Li_(x)NiO₂ and Li_(x)CoO₂ wherein 0<x≦2. Blends can alsoinclude Li_(y)-α-MnO₂ (0≦y<1) which is Li_(y)NH₄Mn₈O₁₆ (0≦y<1) which hasa hollandite-type structure. Li_(y)-α-MnO₂ where 0≦y<0.5 is preferred.α-MnO₂ can be synthesized by precipitation from a reaction between aMnSO₄ solution and (NH₄)₂S₂O₈ as an oxidizing agent.

In a preferred embodiment, the compatible cathodic material of thepresent invention is mixed with a polymeric binder such as describedabove in regard to the anode.

The cathode and anode generally further comprise one or moreelectrically conductive materials. Examples of such materials include,without limitation, graphite, powdered carbon, powdered nickel, metalparticles, and conductive polymers. Conductive polymers arecharacterized by a conjugate network of double bonds. Examples include,without limitation, polypyrrole and polyacetylene.

The invention has been described above with respect to particularpreferred embodiments. Further non-limiting examples of the inventionare given in the examples that follow.

EXAMPLES

General methods for preparation of the various active materials of theinvention will be described in this section. In some cases, materialsprepared in the Examples are further characterized by electrochemicaland other means. The results of such characterization are given in theFigures and the discussion below. A Siemens D500 X-ray Diffractometerequipped with Cu K_(α) radiation (λ=1.54056 Å) was used for X-raydiffraction (XRD) studies of the prepared materials.

The Examples give synthesis schemes for preparing compounds of thegeneral formula

LiM′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

wherein M′ represents a transition metal, M″ represents a valence +3non-transition metal, a and b are independently greater than or equal to0 and less than or equal to 1. That is, in the embodiments exemplifiedbelow, lithium is present in the compounds at a molar amount of unity.It is to be understood that active materials having non-unity values oflithium content can be prepared by using as starting materialsrelatively more or less lithium compound.

To illustrate, compounds of general structureLinM′aM″_(1−a)TibZr_(1−b)O₄ can be prepared according to the Examples byusing as starting material an amount of 0.5 n Li₂CO₃ instead of thelisted 0.5.

Example 1

Preparation of LiVTiO₄ from Li₂CO₃/TiO₂/V₂O₃

The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5V₂O₃→LiVTiO₄+0.5CO₂

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of V₂O₃ is equivalent to 74.94 g

1.740 g of Li₂CO₃ (Pacific Lithium Company), 3.760 g of TiO₂ (AldrichChemical) and 3.530 g of V₂O₃ (Alfa Aesar) were used. The precursorswere initially pre-mixed using a mortar and pestle and the mixture wasthen pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, washard and appeared gray in color with a black metallic sheen.

FIG. 1 shows the x-ray diffraction pattern for this LiVTiO₄ sample. Thedata appear fully consistent with the published data of Arillo et al.,Solid State Ionics volume 107, page 307, published in 1998, for thecompositionally similar LiFeTiO₄. In the Fe material the x-raydiffraction data is consistent for a cubic spinel structure with thespace group Fd3m.

Example 2

Preparation of LiVTiO₄ from LiOH.H₂O/TiO₂/V₂O₃

The general reaction may be summarized:

LiOH.H₂O+TiO₂+0.5V₂O₃→LiVTiO₄+1.5H₂O

1.0 g-mol of LiOH.H₂O is equivalent to 41.96 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of V₂O₃ is equivalent to 74.94 g

1.24 g of LiOH.H₂O (Aldrich Chemical), 2.35 g of TiO₂ (Aldrich Chemical)and 2.21 g of V₂O₃ (Alfa Aesar) were used. The precursors were initiallypre-mixed using a mortar and pestle and the mixture was then pelletized.The pellet was then transferred to a temperature-controlled tube furnaceequipped with an argon gas flow. The sample was heated at a ramp rate of2°/minute to an ultimate temperature of 900° C. and maintained at thistemperature for 8 hours. The sample was then cooled to room temperature,before being removed from the tube furnace for analysis. The powderizedsample showed reasonable uniformity, was hard and appeared black incolor.

FIG. 2 shows the x-ray diffraction pattern for this LiVTiO₄ sample. Thedata appear fully consistent with the published data of Arillo et al.Solid State Ionics 107, 307 (1998) for the compositionally similarLiFeTiO₄. In the Fe material the x-ray diffraction data is consistentfor a cubic spinel structure with the space group Fd3m.

Example 3

Preparation of LiVTiO₄ from Li₂CO₃/TiO₂/V₂O₅ (Under a ReducingAtmosphere)

The general reaction, conducted under a flowing hydrogen atmosphere, maybe summarized:

H₂+0.5Li₂CO₃+TiO₂+0.5V₂O₅→LiVTiO₄+0.5CO₂+H₂O

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of V₂O₅ is equivalent to 90.94 g

1.74 g of Li₂CO₃ (Pacific Lithium Company), 3.76 g of TiO₂ (AldrichChemical) and 4.28 g of V₂O₅ (Alfa Aesar) were used. The precursors wereinitially pre-mixed using a mortar and pestle and the mixture was thenpelletized. The pellet was then transferred to a temperature-controlledtube furnace equipped with a hydrogen gas flow. The sample was heated ata ramp rate of 2°/minute to an ultimate temperature of 900° C. andmaintained at this temperature for 8 hours. The sample was then cooledto room temperature, before being removed from the tube furnace foranalysis. The powderized sample was soft and appeared black in color.

Example 4

Preparation of LiVTiO₄ from Li₂CO₃/TiO₂/V₂O₅ Using CarbothermalReduction

The general reaction, conducted under an inert atmosphere, may besummarized:

0.5Li₂CO₃+TiO₂+0.5V₂O₅+C→LiVTiO₄+0.5CO₂+CO

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of V₂O₅ is equivalent to 90.94 g

The precursors are initially pre-mixed, in the proportions shown above,using a mortar and pestle and then pelletized. The pellet is thentransferred to a temperature-controlled tube furnace equipped with aninert atmosphere gas flow. The sample is then heated at an appropriaterate to an ultimate temperature in the approximate range 650-900° C. Thechosen temperature range assumes the a C→CO carbothermal reductionmechanism. The sample is maintained at this temperature for a time longenough to ensure complete reaction. The sample is then cooled to roomtemperature, before being removed from the tube furnace for analysis.

Example 5

Preparation of LiCrTiO₄ from Li₂CO₃/TiO₂/Cr₂O₃

The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5Cr₂O₃→LiCrTiO₄+0.5CO₂

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of Cr₂O₃ is equivalent to 76.00 g

1.73 g of Li₂CO₃ (Pacific Lithium Company), 3.56 g of TiO₂ (AldrichChemical) and 3.74 g of Cr₂O₃ (Alfa Aesar) were used. The precursorswere initially pre-mixed using a mortar and pestle and the mixture wasthen pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, andappeared yellow/green in color.

FIG. 3 shows the x-ray diffraction pattern for this LiCrTiO₄ sample.Structural refinement gave cubic space group Fd3m, a=8.397 Å, and a unitcell volume of 592.14 Å³. The data appear fully consistent with thepublished data of Arillo et al. Solid State Ionics 107, 307 (1998) forthe compositionally similar LiFeTiO₄. In the Fe material the x-raydiffraction data is consistent for a cubic spinel structure with thespace group Fd3m.

Example 6

Preparation of LiMnTiO₄ from Li₂CO₃/TiO₂/Mn₂O₃

The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5Mn₂O₃→LiMnTiO₄+0.5CO₂

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of Mn₂O₃ is equivalent to 78.94 g

1.70 g of Li₂CO₃ (Pacific Lithium Company), 3.68 g of TiO₂ (AldrichChemical) and 3.63 g of Mn₂O₃ (Alfa Aesar) were used. The precursorswere initially pre-mixed using a mortar and pestle and the mixture wasthen pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, wassemi-hard and appeared black/gray in color.

FIG. 4 shows the x-ray diffraction pattern for this LiMnTiO₄ sample. Thedata appear fully consistent with the published data of Arillo et al.Solid State Ionics 107, 307 (1998) for the compositionally similarLiFeTiO₄. In the Fe material the x-ray diffraction data is consistentfor a cubic spinel structure with the space group Fd3m.

Example 7

Preparation of LiFeTiO₄ from Li₂CO₃/TiO₂/Fe₂O₃

The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.5Fe₂O₃→LiFeTiO₄+0.5CO₂

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.5 g-mol of Fe₂O₃ is equivalent to 79.85 g

1.69 g of Li₂CO₃ (Pacific Lithium Company), 3.66 g of TiO₂ (AldrichChemical) and 3.66 g of Fe₂O₃ (Aldrich Chemical) were used. Theprecursors were initially pre-mixed using a mortar and pestle and themixture was then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with an argon gas flow. Thesample was heated at a ramp rate of 2°/minute to an ultimate temperatureof 900° C. and maintained at this temperature for 8 hours. The samplewas then cooled to room temperature, before being removed from the tubefurnace for analysis. The powderized sample showed good uniformity, wasvery hard and appeared brick red in color.

FIG. 5 shows the x-ray diffraction pattern for this LiFeTiO₄ sample.Structural refinement gives cubic space group Fd3m, a=8.432 Å and a unitcell volume of 581.96 Å3. This is isostructural with the published dataof Arillo et al. Solid State Ionics 107, 307 (1998) for their ownprepared LiFeTiO₄ material.

Example 8

Preparation of LiCoTiO₄ from LiCoO₂/TiO₂

The general reaction may be summarized:

LiCoO₂+TiO₂→LiCoTiO₄

1.0 g-mol of LiCoO₂ is equivalent to 97.87 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

4.40 g of LiCoO₂ (Sherrett-Westaim Company) and 3.60 g of TiO₂ (AldrichChemical) were used. The precursors were initially pre-mixed using amortar and pestle and the mixture was then pelletized. The pellet wasthen transferred to a temperature-controlled tube furnace equipped withan argon gas flow. The sample was heated at a ramp rate of 2°/minute toan ultimate temperature of 900° C. and maintained at this temperaturefor 8 hours. The sample was then cooled to room temperature, beforebeing removed from the tube furnace for analysis. The powderized sampleshowed good uniformity, was very hard and appeared turquoise blue-greenin color.

FIG. 6 shows the x-ray diffraction pattern for this LiCoTiO₄ sample. Thedata appear fully consistent with the published data of Arillo et al.Solid State Ionics 107, 307 (1998) for the compositionally similarLiFeTiO₄. In the Fe material the x-ray diffraction data is consistentfor a cubic spinel structure with the space group Fd3m.

Example 9

Preparation of LiNiTiO₄ from Li₂CO₃/TiO₂/2NiCO₃.3Ni(OH)₂.4H₂O

The general reaction may be summarized:

0.5Li₂CO₃+TiO₂+0.2[2NiCO₃.3Ni(OH)₂.4H₂O]→LiNiTiO₄+0.9CO₂+1.4H₂O

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g

1.0 g-mol of TiO₂ is equivalent to 79.88 g

0.2 g-mol of 2NiCO₃.3Ni(OH)₂.4H₂O is equivalent to 117.5 g

2.08 g of Li₂CO₃ (Pacific Lithium Company), 4.49 g of TiO₂ (AldrichChemical) and 6.63 g of 2NiCO₃.3Ni(OH)2.4H₂O (Aldrich Chemical) wereused. The precursors were initially pre-mixed using a mortar and pestleand the mixture was then pelletized. The pellet was then transferred toa temperature-controlled tube furnace equipped with an oxygen gas flow.The sample was heated at a ramp rate of 2°/minute to an ultimatetemperature of 850° C. and maintained at this temperature for 8 hours.The sample was then cooled to room temperature, before being removedfrom the tube furnace for analysis. The powderized sample showedreasonable uniformity, was soft and appeared mainly yellow in color.

Example 10

Preparation of LiMZrO₄ from Li₂CO₃/ZrO₂/M₂O₃

The general reaction may be summarized:

0.5Li₂CO₃+ZrO₂+0.5M₂O₃→LiMZrO₄+0.5CO₂.

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g.

1.0 g-mol of ZrO₂ is equivalent to 123.22 g.

0.5 g-mol of M₂O₃ varies according to M.

The reaction is carried out according to the conditions of Example 1.Preferably, the temperature of reaction is above 1000° to react theZrO₂.

Example 11

Preparation of LiMZr_(1−x)Ti_(x)O₄ from Li₂CO₃/TiO₂/ZrO₂/M₂O₃

The general scheme is0.5Li₂CO₃+(1−x)ZrO₂+xTiO₂+0.5M₂O₃→LiMZr_(1−x)Ti_(x)O₄

The reaction for x=0.5 may be summarized:

0.5Li₂CO₃+0.5ZrO₂+0.5TiO₂+0.5M₂O₃→LiMZr_(0.5)Ti_(0.5)O₄

0.5 g-mol of Li₂CO₃ is equivalent to 36.95 g.

0.5 g-mol of ZrO₂ is equivalent to 61.61 g.

0.5 g-mol of TiO₂ is equivalent to 39.94 g.

0.5 g-mol of M₂O₃ varies according to M.

The reaction is carried out according to the conditions of Example 1.Preferably, the temperature of reaction is above 1000° to react theZrO₂.

Example 12

Preparation of LiMZr_(1−x)Ti_(x)O_(x)—Using Hydrogen

The general reaction for x=0.5 and for M=vanadium may be summarized.

0.5Li₂CO₃+0.5ZrO₂+0.5TiO₂+0.5V₂O₅+H₂→LiMZr_(0.5)Ti _(0.5)O₄+0.5CO₂+H₂O

0.5 g-mol of Li₂CO₃=36.95 g

0.5 g-mol of ZrO₂=61.61 g

0.5 g-mol of TiO₂=39.94 g

0.5 g-mol of V₂O₅=90.94 g

The reaction is carried out according to Example 3. Preferably, thetemperature of reaction is above 1000° to react the ZrO₂.

Example 13

Preparation of LiMZr_(1−x)Ti_(x)O₄ by Carbothermal Reduction

The general reaction for the case where M is vanadium may be summarized:

0.5Li₂CO₃+(1−x)ZrO₂+xTiO₂+0.5V₂O₅+C→LiVZr_(1−x)Ti _(x)O₄+0.5CO₂+CO

For x=0.5:

0.5 g-mol of Li₂CO₃=36.95 g

0.5 g-mol of ZrO₂=61.61 g

0.5 g-mol of TiO₂=39.94 g

0.5 g-mol of V₂O₅=90.94 g

1.0 g-mol of carbon=12.00 g

The reaction is carried out according to Example 4. Assumes C →COreaction scheme for carbothermal reduction. Excess carbon, for exampleup to 100% weight excess, may be used. Preferably, the temperature ofreaction is in the range of 700-1050° C.

Example 14

Preparation of LiM′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄

Examples of non-transition metals: B, Al, Ga and In, all of which arenormally available as M″₂O₃ oxides e.g. Al(OH)₃, Ga(OH₃), In(OH)₃. Theyare also available as M″(OH)₃ hydroxides, e.g., Al(OH)₃, Ga(OH)₃ andIn(OH)₃.

The general reaction scheme is:

The reaction requires:

0.5 g-mol of Li₂CO₃

(1−b) g-mol of ZrO₂

(b) g-mol of TiO₂

a/2 g-mol of M′₂O₃

(1−a)/2 g-mol of M″₂O₃

Reaction is carried out as in Example 1. A temperature above 1000° C.may be necessary to react ZrO₂.

Electrochemical Characterization of Active Materials

For electrochemical evaluation purposes the active materials were cycledagainst a lithium metal counter electrode. The active materials wereused to formulate the positive electrode. The electrode was fabricatedby solvent casting a slurry of the active material, conductive carbon,binder and solvent. The conductive carbon used was Super P (MMM Carbon).Kynar® Flex 2801 was used as the binder and electronic grade acetone wasused as the solvent. The slurry was cast onto glass and a free-standingelectrode film was formed as the solvent evaporated. The proportions areas follows on a weight basis: 80% active material; 8% Super P carbon;and 12% Kynar binder.

For all electrochemical measurements the liquid electrolyte was ethylenecarbonate/dimethyl carbonate, EC/DMC (2:1 by weight) and 1 M LiPF6. Thiswas used in conjunction with a Glass Fiber filter to form theanode-cathode separator. Routine electrochemical testing was carried outon a commercial battery cycler using constant current cycling betweenpre-set voltage limits. High-resolution electrochemical data werecollected using the Electrochemical Voltage Spectroscopy (EVS)technique. Such technique is known in the art as described in Synth.Met. D217 (1989); Synth. Met. 32, 43 (1989); J. Power Sources, 52,185(1994); and Electrochimica Acta 40, 1603 (1995).

Electrochemical Characterization of LiVTiO₄

FIG. 7 (Cell#908086) shows the first cycle constant current data of theLiVTiO₄ material made from Li₂CO₃/TiO₂/V₂O₃. The data were collectedusing a lithium metal counter electrode at 0.2 mA/cm² between 2.00 and4.00 V and are based upon 27.2 mg of the LiVTiO₄ active material in thepositive electrode. The testing was carried out at 23° C. The initialmeasured open circuit voltage (OCV) was approximately 2.70 V vs. Li.Lithium is extracted from the LiVTiO₄ during charging of the cell. Acharge equivalent to a material specific capacity of 84 mAh/g isextracted from the cell. The theoretical specific capacity for LiVTiO₄(assuming all the lithium is extracted) is 158 mAh/g. Consequently, thepositive electrode active material corresponds to Li_(1−x)VTiO₄ where xequates to about 0.53, when the active material is charged to about 4.00V vs. Li. When the cell is discharged to approximately 2.00 V a quantityof lithium is re-inserted into the Li_(1−x)VTiO₄. The re-insertionprocess corresponds to approximately 87 mAh/g, indicating a goodreversibility of the LiVTiO₄ material. At 2.00 V the positive activematerial corresponds to approximately Li_(1.02)VTiO₄. The generallysymmetrical nature of the charge-discharge curves further indicates thegood reversibility of the system.

The LiVTiO₄ material made from Li₂CO₃/TiO₂/V₂O₃ was further subjected tohigh resolution electrochemical testing using the ElectrochemicalVoltage Spectroscopy (EVS) technique. FIG. 8 shows the electrode voltageversus specific capacity data for this material when cycled betweenvoltage limits of 2.40 and 3.40 V. The weight of the active material was35.3 mg and the test was carried out at 23° C. A charge equivalent to amaterial specific capacity of 82 mAh/g is extracted from the cell. Thus,when fully charged the positive electrode active material, representedby Li_(1−x)VTiO₄, corresponds to Li_(0.48)VTiO₄. The re-insertionprocess corresponds to approximately 78 mAh/g, indicating a goodreversibility of the LiVTiO₄ material. The capacity corresponding to thelithium extraction process is essentially the same as the capacitycorresponding to the subsequent lithium insertion process. Thus, thereis essentially no capacity loss. FIG. 9, the differential capacity data,also indicates good reversibility. The symmetrical nature of the peaksindicates the good electrochemical reversibility. Further, there is lowpeak separation (charge/discharge) and good correspondence between thebroad peak above and below the zero axis. There are essentially no peaksthat can be related to irreversible reactions. Overall, this EVS testdemonstrates that the preparative procedure used to make this materialproduces a high quality electrode material.

FIG. 10 (Cell#908087) shows the first cycle constant current data of theLiVTiO₄ material made from LiOH.H₂O/TiO₂/V₂O₃. The data were collectedusing a lithium metal counter electrode at 0.2 mA/cm² between 2.00 and4.00 V and are based upon 22.6 mg of the LiVTiO₄ active material in thepositive electrode. The testing was carried out at 23° C. The initialmeasured open circuit voltage (OCV) was approximately 2.80 V vs. Li.Lithium is extracted from the LiVTiO₄ during charging of the cell. Acharge equivalent to a material specific capacity of 80 mAh/g isextracted from the cell. The theoretical specific capacity for LiVTiO₄(assuming all the lithium is extracted) is 158 mAh/g. Consequently, thepositive electrode active material corresponds to Li_(1−x)VTiO₄ where xequates to about 0.51, when the active material is charged to about 4.00V vs. Li. When the cell is discharged to approximately 2.00 V a quantityof lithium is re-inserted into the Li_(1−x)VTiO₄. The re-insertionprocess corresponds to approximately 79 mAh/g, indicating excellentreversibility of the LiVTiO₄ material. At 2.00 V the positive activematerial corresponds to approximately Li_(1.00)VTiO₄. The generallysymmetrical nature of the charge-discharge curves further indicates thegood reversibility of the system. The data collected from this materialis fully consistent with the equivalent data collected—shown above—forthe LiVTiO₄ made from Li₂CO₃/TiO₂/V₂O₃ route.

It has been noted above that about 50% of the available lithium isextracted from the LiVTiO₄ structure. Without being bound by theory, itis likely that the structure of all LiMTiO₄ materials may becharacterized as cubic spinel with the space group Fd3m. The cubicspinel structure, A[B₂]O4 is characterized by cubic-closed packed oxygenions occupying the 32e sites, the A cations located in the tetrahedral 8a sites and the B cations located in octahedral 16 d sites. This is thesame structure as the lithiated manganese spinel LiMn₂O₄, the well-knowncathode active material used in commercial lithium ion applications. Instoichiometric LiMn₂O₄ spinel, in which the alkali metal cations are alllocated in the tetrahedral 8 a sites and the Mn cations occupy theoctahedral 16 c sites, it is possible to extract almost all the lithiumfrom the structure. In the paper by Arillo et al. it is reported that inthe LiFeTiO₄ structure there exists a different situation in which thereis a distribution of alkali metal cations over both the 8 a and 16 csites. Thus, only about 50% of the lithium cations are actually locatedon the tetrahedral 8 a sites, the remaining lithium cations located inthe octahedral sites. This suggests that only around half the lithiumions will be available for extraction and therefore only 50% of thetheoretical specific capacity would be realized in operation. This isclose to what is observed experimentally in this work.

Electrochemical Characterization of LiCrTiO₄

The LiCrTiO₄ material made from Li₂CO₃/TiO₂/Cr₂O₃ was tested using theElectrochemical Voltage Spectroscopy (EVS) technique. FIG. 11 shows theelectrode voltage versus specific capacity data for this material whencycled between voltage limits of 3.40 and 4.80 V. The weight of theactive material was 11.1 mg and the test was carried out at 23° C. Acharge equivalent to a material specific capacity of 37 mAh/g isextracted from the cell. The re-insertion process corresponds toapproximately 13 mAh/g, indicating a relatively high irreversiblecapacity loss for the EVS cycle. Bearing in mind the extremely highoperating voltage for this material—around 4.6 V vs. Li—the level ofirreversibility is not surprising. At such extreme operating potentialsit is well known that the electrochemical system will become veryunstable. Several irreversible reactions will be expected to occur, suchas electrolyte solvent electrolysis, electrode binder breakdown, as wellas positive electrode current-collector degradation. These factors willdetrimentally affect the experimental results. What is particularlyinteresting is the fact that there still exists significant (reversible)electrode activity at such high potentials. Indeed, it is probable thatin a more stable electrolyte system a significantly higher specificcapacity would be realized. There are very few known insertion materialsthat can operate at such oxidative conditions as those shown here forthe LiCrTiO₄.

FIG. 12, the differential capacity data, also indicates the LiCrTiO₄material insertion activity. Close inspection of this figure allows thereversible insertion reactions to be resolved—part of the broad chargepeak above the x-axis is clearly reversible during the insertion processshown below the x-axis. However, as expected from the high irreversiblecapacity loss described in FIG. 10, there are clearly othernon-reversible reactions also occurring during the cycle.

In separate experiments the discharge or lithium insertion properties ofthe as-made LiCrTiO₄ material were probed. Such measurements are usefulin determining the low voltage insertion behavior of materials in orderto evaluate these compounds as potential negative (anode) materials forlithium ion cells. In such trials on the LiCrTiO₄ material, threepossible reduction reactions may be proposed:

LiCr³⁺Ti⁴⁺O₄+Li⁺+e→Li₂Cr²⁺Ti⁴⁺O₄  (1)

LiCr³⁺Ti⁴⁺O₄+2Li⁺+2e→Li₃Cr³+Ti²⁺O₄  (2)

 LiCr³⁺Ti⁴⁺O₄+3Li⁺+3e→Li₄Cr²⁺Ti²⁺O₄  (3)

Based on a molecular mass of 170.8 for LiCrTiO₄, approximate specificcapacities of 157 mAh/g, 314 mAh/g and 471 mAh/g may be calculated forthe reactions (1), (2) and (3) respectively.

The anode properties of the LiCrTiO₄ material were probed using the EVSmethod. FIG. 13 shows the electrode voltage versus specific capacitydata for the LiCrTiO₄ material when cycled between voltage limits of2.00 and 1.00 V. The weight of the active material was 22.2 mg and thetest was carried out at 23° C. During the discharge process the activematerial may be represented as Li_(1+x)CrTiO₄ indicating the increasingamount of Li in the structure. The material demonstrates a flat voltageplateau at around 1.5 V vs. Li, indicating the insertion of lithium intothe structure. The discharge process is equivalent to a specificcapacity of around 103 mAh/g and based on its molecular mass, thestoicheometry of the active material when discharged to 1.00 V, may beestimated as Li_(1.66)CrTiO₄. When subsequently charged to 2.00 V, acharge equivalent to a material specific capacity of 94 mAh/g isextracted from the cell indicating the excellent reversibility of theLiCrTiO₄ material. In the fully charged state, the active materialcorresponds to approximately Li_(1.06)CrTiO₄. The generally symmetricalnature of the charge-discharge curve, and the small voltage difference,further indicates the good reversibility of the system.

FIG. 14, the differential capacity data, indicates excellentreversibility. The symmetrical nature of the peaks indicates goodelectrochemical reversibility; there is very small peak separation(discharge/charge) and good correspondence between peaks above and belowthe zero axis. There are essentially no peaks that can be related toirreversible reactions, since the peak above the axis (cell charge) hasa corresponding peak below the axis (cell discharge). These datademonstrate that the preparative procedure used to make this materialproduces a high quality electrode material.

We claim:
 1. An electrode active material, comprising a cubic spinelstructure and represented by the general formulaLi_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄, wherein: n is from about 0.01 to2, a is greater than or equal to 0 and less than or equal to 1, b isgreater than or equal to 0 and less than or equal to 1, M′ is selectedfrom the group consisting of transition metals and mixtures thereof,with the proviso that when b is 1, M′ comprises at least vanadium, andM″ is selected from the group consisting of valence +3 non-transitionmetals and mixtures thereof.
 2. The electrode active material accordingto claim 1, wherein M′ is selected from the group consisting oftitanium, vanadium, manganese, iron, chromium, nickel, cobalt,molybdenum, niobium, and combinations thereof.
 3. The electrode activematerial according to claim 2, wherein M″ is selected from the groupconsisting of aluminum, boron, indium, gallium, antimony, bismuth,thallium, and combinations thereof.
 4. The electrode active materialaccording to claim 3, wherein a is greater than 0 and less than
 1. 5.The electrode active material according to claim 4, wherein b is greaterthan 0 and less than
 1. 6. The electrode active material according toclaim 3, wherein b is greater than 0 and less than
 1. 7. The electrodeactive material according to claim 1, wherein a is greater than 0 andless than
 1. 8. The electrode active material according to claim 7,wherein b is greater than 0 and less than
 1. 9. The electrode activematerial according to claim 1, wherein b is greater than 0 and lessthan
 1. 10. The electrode active material according to claim 1, whereinn is 0.2 to
 2. 11. The electrode active material according to claim 1,wherein n is 0.5 to
 2. 12. The electrode active material according toclaim 1, wherein n is
 1. 13. The electrode active material according toclaim 1, wherein the electrode active material is represented by theformula Li_(n)VTiO₄.
 14. The electrode active material according toclaim 13, wherein n is 0.2 to
 2. 15. The electrode active materialaccording to claim 13, wherein n is 0.5 to
 2. 16. The electrode activematerial according to claim 13, wherein n is
 1. 17. An electrode,comprising an active material having a cubic spinel structure andrepresented by the general formulaLi_(n)M′_(a)M″_(1−a)Ti_(1−b)Zr_(1−b)O₄ wherein n is from about 0.01 to2, a is greater than or equal to 0 and less than or equal to 1, b isgreater than or equal to 0 and less than or equal to 1, M′ is selectedfrom the group consisting of transition metals and mixtures thereof,with the proviso that when b is 1, M′ comprises at least vanadium, andM″ is selected from the group consisting of valence +3 non-transitionmetals and mixtures thereof.
 18. The electrode according to claim 17,wherein M′ is selected from the group consisting of titanium, vanadium,manganese, iron, chromium, nickel, cobalt, molybdenum, niobium, andcombinations thereof.
 19. The electrode according to claim 18, whereinM″ is selected from the group consisting of aluminum, boron, indium,gallium, antimony, bismuth, thallium, and combinations thereof.
 20. Theelectrode according to claim 19, wherein a is greater than 0 and lessthan
 1. 21. The electrode according to claim 20, wherein b is greaterthan 0 and less than
 1. 22. The electrode according to claim 19, whereinb is greater than 0 and less than
 1. 23. The electrode according toclaim 17, wherein a is greater than 0 and less than
 1. 24. The electrodeaccording to claim 23, wherein b is greater than 0 and less than
 1. 25.The electrode according to claim 17, wherein b is greater than 0 andless than
 1. 26. The electrode according to claim 17, wherein n is 0.2to
 2. 27. The electrode according to claim 17, wherein n is 0.5 to 2.28. The electrode according to claim 17, wherein n is
 1. 29. Theelectrode according to claim 17, wherein the active material isrepresented by the formula Li_(n)VTiO₄.
 30. The electrode according toclaim 29, wherein n is 0.2 to
 2. 31. The electrode according to claim29, wherein n is 0.5 to
 2. 32. The electrode according to claim 29,wherein n is
 1. 33. The electrode according to claim 17, furthercomprising an electrically conductive material.
 34. The electrodeaccording to claim 33, wherein the electrically conductive material isselected from the group consisting of graphite, powdered carbon,powdered nickel, metal particles, and conductive polymers.
 35. Abattery, comprising: a cathode comprising an active material having acubic spinel structure and represented by the general formulaLi_(n)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄ wherein: n is from about 0.01 to 2,a is greater than zero and less than 1, b is greater than or equal to 0and less than or equal to 1, M′ is selected from the group consisting oftransition metals and mixtures thereof, the proviso that when b is 1, M′comprises at least vanadium, and M″ is selected from the groupconsisting of valence +3 non-transition metals and mixtures thereof; thebattery further comprising an anode; and an electrolyte.
 36. The batteryaccording to claim 35, wherein M′ is selected from the group consistingof titanium, vanadium, manganese, iron, chromium, nickel, cobalt,molybdenum, niobium, and combinations thereof.
 37. The battery accordingto claim 36, wherein M″ is selected from the group consisting ofaluminum, boron, indium, gallium, antimony, bismuth, thallium, andcombinations thereof.
 38. The battery according to claim 37, wherein ais greater than 0 and less than
 1. 39. The battery according to claim38, wherein b is greater than 0 and less than
 1. 40. The batteryaccording to claim 35, wherein b is greater than 0 and less than
 1. 41.The battery according to claim 35, wherein a is greater than 0 and lessthan
 1. 42. The battery according to claim 41, wherein b is greater than0 and less than
 1. 43. The battery according to claim 35, wherein b isgreater than 0 and less than
 1. 44. The battery according to claim 35,wherein n is 0.2 to
 2. 45. The battery according to claim 35, wherein nis 0.5 to
 2. 46. The battery according to claim 35, wherein n is
 1. 47.The battery according to claim 35, wherein the active material isrepresented by the formula Li_(n)VTiO₄.
 48. The battery according toclaim 47, wherein n is 0.2 to
 2. 49. The battery according to claim 47,wherein n is 0.5 to
 2. 50. The battery according to claim 47, wherein nis
 1. 51. The battery according to claim 35, wherein the active materialis represented by the general formulaLi_(n−c)M′_(a)M″_(1−a)Ti_(b)Zr_(1−b)O₄ wherein in a first condition c iszero, and in a second condition c is greater than zero and less than n.52. The battery according to claim 51, wherein the first conditioncorresponds to an uncharged state and the second condition correspondsto a charged or partially charged state.
 53. The battery according toclaim 35, wherein the cathode further comprises an electricallyconductive material.
 54. The battery according to claim 53, wherein theelectrically conductive material is selected from the group consistingof graphite, powdered carbon, powdered nickel, metal particles, andconductive polymers.
 55. The battery according to claim 53, wherein thecathode further comprises a binder.
 56. The battery according to claim35, wherein the anode is a lithium insertion anode.
 57. The batteryaccording to claim 35, wherein the anode comprises a carbon material.58. The battery according to claim 35, wherein the anode comprises anactive material represented by the formula Li_(n+c)MTiO₄ wherein n isfrom 0.01 to about 2; M is a transition metal; and in a first conditionc is 0, and in a second condition, c is greater than
 0. 59. The batteryaccording to claim 58, wherein M is selected from the group consistingof vanadium, manganese, iron, chromium, nickel, cobalt, molybdenum,niobium, and combinations thereof.